Electronic devices are essentially three dimensional structures of electrically conductive and electrically insulating materials. Such electronic devices include not only equipment but also sub assemblies, printed circuit boards (PCBs), both bare and assembled, and individual components such as integrated circuits and transistors. The electrically conductive parts of such structures usually consist of metals such as copper, aluminum, silver, gold, conductive polymers, semiconductor materials, etc. The electrically non-conductive parts or insulators of these structures usually consist of polymers such as polyimide, polytetrafluoroethylene, silicone, or polyamide, with or without glass-fiber reinforcement, paper based materials, ceramics, glass, etc.
Throughout the lifetime of assembled electronic devices, they are subject to various forms of contamination. The conductivity of some of the materials may be reduced by atmospheric corrosion, and pollution can cause conductive paths to become established between adjacent traces or conductors. Additionally, electronic devices can often accidentally be submersed in various liquids, such as water, often destroying the function of the electronic device. As electronic devices are being used increasingly in more and more hostile and polluted environments, there has become a greater need to protect these items from damage when exposed to those environments.